Tories



March 15, 1927. l,,620,631

c. A. BRIGHAM ELECTROMAGNETIC SOUND REPRODUCER Filed Sept. 13, 1926 I 4 Sheets-Sheet l W a 4mg.

ATTORNEY j EYE-77.1

March 15,1927.

ELECTROMAGNETIC c. A. BRIGHAM SOUND REPRODUCER Filed Sept. 15, 1926 4 Sheets-Sheet 2 IN VEN TOR.

March 15,1927. 1,620,631

a. A: BRIGHAM ELECTROMAGNETI C SOUND REPRODUCER Filed Sept. 13, 1926 4 Sheets-Sheet 5 mmi" Iii l W @M 6Q ATTORNEY March 15,1927" 1,620,631

G. A. BRHGHAM ELECTROMAGNETIC SOUND REPRODUCER Filed Sept. 1 1926 4 Sheets-Sheet 4 INVENTOR.

ATTORNEY Patented Mar. 15, 1927.

UNITED STATES PATENT FFICE.

CYRIL A. BRIGI-IAM, OF EAST ORANGE, NEW JERSEY, ASSIGNGR T0 BRANDES LABORA TORIES, INCL, OF NEWARK, NEW JERSEY, A CORPORATION OF NEN JERSEY.

ELECTROMAGNETIC SOUND Application filed September 13, 1926.

My invention relates broadly to electromagnetic sound reproducers and more particularly to a construction of power type loud speaker reproducer tor the accurate reproduction of articulate speech and music.

One of the objects o't my invention is to provide a loud speaker rcproducer having; parts arranged for the reproduction of sound at large amplitude with substantially no distortion.

Another object of my invention is to pro vide a loud speaker reproducer which does not employ a magnetic armature member as the movable element of the loud speaker, but which in lieu thereof is provided with a flat coil structure of extremely small mass which is connected in the output circuit of an an'iplilier, system and which is longitudinally movable within an intense magnetic field.

still further object of my invention is to provide a substantially (listortionless sound reproducer having means for changing the reactancc ot the reproducing circuit in proportion to variatioi'is in frequency of the incon'ling signaling ei'iergy for the faithful reproduction of sound.

A still further object of my invention resides in the arrangement ot a flat coil with in an intense magnetic field with conductire plate .u'leiubers positioned on opposite sides of the movable coil member for changinn, the reactance of the movable coil in proportion to the varia ion in frequency of the incoming signaling energy for main taining the operating characteristic of the sound reproducer in a substantially uniform condition.

Still another object of my invention is to provide a loud speaker reproducer having movablememher vibratile in accordance with electrical vibrations which. movable member has a natural period far removed from the normal voice or music frequencies.

Still another objectof my invention is to provide a construction of sound reproducer employing a fiat longitudinal movable member which connects with a sound re REPRODUCER.

Serial N0. 135,192.

producing diaphragm for imparting vibrations thereto for the reproduction of sound at large amplitude.

My invention will be more clearly under stood by reference to the accompanying drawings wherein:

Figure 1 is a rear view of the assembed power speaker of my invention; Fig. 2 is a top plan view of the power speaker; Fig. 3

is a side elevation of the power speaker with parts of the sound reproducing diaphragm and support therefor broken away and illustrated in cross-section; Fig. 4 is a cross-sectional view through the power s 'ieaker taken on line H of Fig. 2 and showingthe flat longitudinal movable coil member employed in the power speaker; Fig. 5 is a perspective view of one of the conductive plate members which I provide in association with the pole pieces of the power speaker: Fig. 6 is a fragmentary cross-sectional view taken through the electron'iagnetic operating structure of the power speaker; Fig. 7 is a side view of the insulziitod structure on which the driving coils are supported; Fig. 8 is a plan view of the driving coil assembled upon the insulated structure of Fig. 7 Fig. 9 is a cross-sectional view through the driving member taken on line 9-9 of Fig. 8; Fig. '10 is an enlarged cross-sectional view through the driving coils taken on line l0--10 of Fig, 8: Figs. 11 and 12 are front and sectional views of one of the spiders for suspending the driving coils for movement between the pole pieces of the electromagnetic system; and Figs. 13 and 14 show front and sectional views of the end mem bers upon which the spiders are mounted for centering the driving coils between the pole pieces.

Heretofore in the art it has been customary to employ a type of electromagnetic driving mechanism for sound reproducers where a daphragm or armature has generally been employed as the vibrating element. The method of mounting or clamping the armacure or diaphragm for operation in the sound reproducer and the physical dimensions thereof have il'ltl'OClllCGtl very marked limitations in the operating charactcristics of such electromagnetic reproduccrs. The physical structures have inherently introi'luced strong mechanical resonances which are detrimental to the correct response ol the reproducer over the complete frequency range emountered in radio broadcast reception thereby impairing: the quality of the reproduction.

Realizing the serious limitation offered by mechanical resonances oi. the arn'iatnre or diaphragm in an electromagrn-ctic sound reprodncern I ha \e devmed an electromagnietic sound reproducing system having a vibratory element therein operating substantially independcntly ol" ineclninical rcsmnuu'es. I provide an electron:acnetic lield relatively large strength and in this tield suspend a 'tlat movable coil member ot extremely light.

weight. The signaling} cum" is introduced into the movable coil member which is mechanically vibrated for imparting): movement to a sound reproducing diaphr: an. it provide a novel method ol' suspend mr the morable coil member whereby longitudinal morement of the coil member between the pole pieces of the electromagnetic system may be efl'ected without change in the spacial relation between the sides of the n'iovable coil and the "pole pieces. In order to improve the ope 'ating characteristics of the power speaker I provide conductive shields adjacent the pole pieces and the movable coil. in which shields eddy currents are introduced for changing the reactance of the coil system at higher frequencies for insuring a more uniform reproduction ot musical notes over the entire frequency range.

Referring to the drawings in more detail I have represented the power speaker as suspended from the top l of a cabinet structure by means of bolt members 2 to which brackets 3 are secured. The power speaker consists of a frame structure made up of plate members at and .5 clamped at opposite ends by means of bolt members 9 and it) on opposite sides of the lamina-ted magnetic core structure 1]. with spacer members 6 lie-- tween the surfaces of panels 4t and 5 and the core structure. The plate members 4: and 5 are cut away at their central portions as represented at at and 5* and the supporting plates 7 secured thereto From which the spider members 8 are suspended.

The spider members 8 are shaped as represented more clearly in Figs. l and 11 ha vmg a pair of side suspension arms 8 ant 8 and a pair of central arms 8 and 8" extending in opposite directions along the axis thereof for supporting the flat form 12 in a plane which passes through the power speaker between the pole tips l l and 15 which-extend from the laminated core members 11 on which the electromagnetic windings 1.6 and 1? are carried. The pole pieces M and 15 are clamped by means of strip members l8 and 19 by boltn'iembers LS and 19 forming a rigid structure. The pole pieces are encased in conductive cap members 2t) and 21 each of the cap members having cut away portions 2i) and 20" and 21 and 21 into which the pole pieces fit.

in Fig. I have illustrated in perspective view one of the caps 20 having pockets E20 and 20" therein to receive the pole pieces and present a Hat conductive surface closely parallel to the coil. form 12.

The coil term 12 is construz'zted of extremely light weight insulating material and is substantially in the term ot a skeleton upon which coils 22 and 28 are supported on opposite sides thereo't. 'llhese coils are wound s1ibstantially flat and secured to opposite sides of the coil form iii. The coils are relatively narrow in width. seldom beiiug' more than one-halt inch wide. Aluminum wire is chosen for securing the lightest possible weight in the driving system. The oils 22 and 23 are secured to the flat surtaces ot the coil term 12 and are secured to'each other. as represented at 2th. beyond the limits of the coil form 12. The coil form 12 is provided with projecting studs 12, 12, 12 and 12 by which the coil term is supported between the soider 8 and by which the driving "forces may be delivered from the longitudinally vibratile coil to the sound reproducing diaphragm.

By reason of the flat construction of the driving coil the spacial relation or gap between the sides of the coils E22 and 23 and the conductive plate men'ibers 20 and 21. may be maintained extremely small.

1 provide COllllGCt'lllf-l' l'nembers ot aluminum represented in Fig. 4 at 25, 25, 25 and 25 which are secured over the studs 11L 132 12 and lil ot the coil support l2 tor aligning the coil support with the ends of the spider arms 8"" and 8 and suspendil'ig the coils for lateral II'IOVQll'lGllt with respect to the pole pieces I l; and l5. [in aluinimnn connecting member 233 is secured to the stud l2 to which a rod member 26 is connected passing through the aperture 8"- in the spider 8 and connecting to the apex piece of the sound reproducing; diaphragm 38. The sound. lfClDI'Otlllt'lllg diaphragm is illus trated as consisting; of an elliptically shaped fibrous surface snbstai'itially tree to vibrate at its peripheral edge by virtue of the flexible suspension 29 by which the peripheral edge 30 of the diaphragm is suspended within the elliptical aperture 3t of the plate The plate 32 is supported from the "frame of the power speaker by means of brackets 33 forming a rugged structure.

The construction. of the spider men'ibers 8 he resultof extended research and developement for securing strictly lateral movement of the vibratory coils E22 and 23 Ill) lli') tit) without side wiping with respect to the pole pieces or the conductive plate members and 21.

The field windings 16 and 17 are excited from a suitable source of direct current and the signaling current from the output of the loud speaker electron tube amplifier, connected with the signal receiving apparatus supplied to the coils 22 and 23. The connection of the coils 22 and 23 with the output circuit of the power amplifier is such that the signaling current passes through the two coils in parallel. The elctromagnets comprising the field windings are connected in series in such manner that opposite poles are directed toward each other for creating a flux which cuts the turns of the windings on the movable coil support whereby a driving torque is developed which tends to move the vibratory coil. at right angles with re spect to the concentrated field between the pole pieces 14 and 15. The position of the plates 20 and 21. serves to change the reactance of the driving coils at the higher frequencies rendering the operating characteristics of the loud speaker system more uniform over the entire range of musical notes.

The embodiment of my invention illustrated in the drawings has been found to be very practical in construction and capable of manufacture and production on a quantity basis with uniform characteristics in the many loud speakers passing through a production program.

The operation of the power speaker is such that the reproduction is extremely faithful with respect to the modulation at the broadcasting station inasmuch as the mechanical. resonances in the reproducing system have been eliminated.

While I have described my invention in certain pre terred embodiments, I desire that it he understood that modifications may be made and that no limitations upon the inveution are intended other than are imposed by the scope of the appended claims.

l'V ha t T claim as new and desire to s cure by l letlers Patent oi the United Flt-ates as folio we I 1. In an electromagnetic sound reproducing apparatus an electromagnetic field system including a plurality of pole pieces di rected toward each other and separated by a gap, pair of eenductire members positioned over said pole pieces forming sub stantially parallel walls, a flat coil member resiliently suspended betweeen said parallel walls, a sound. reproducing diaphragm mechanically connected with said flat coil memher. said coil member being energized by variable signal currents for the setting up of mechanical vibrations in a direction substantially normal to the direction of said pole pieces whereby corresponding vibrations are imparted to said sound reproducing diaphragm.

2. In an electromagnetic sound reproducer, an electromagnetic operating system including a plurality of pole pieces directed toward each other and separated by a narrow gap, a flat insulated coil support flex bly suspended in said gap, a flat coil member disposed on each side of said fiat coil support, a sound reproducing diaphragm, a connection between said sound reproducing diaphragm and said flat coil support, said coil members being energized by variable ignaling current whereby said coil support is subjected to mechanical vibrations in a direction substantially normal to the direction of said pole pieces for imparting corresponding vibrations to sound reproducing diaphragm,

3. in an electrmnagnetic sound reproducing system an electromagnetic field including a plurality of pole pieces directed toward each other and seynrrated by a gap, a sound reproducing diaphragm and a Hat coil. structure disposed in said gap and mechanically connected with said sound reproducing diaphragm, means for flexibly mounting said list coil structure at'opposite ends thereof for lateral movement in said gap in a line substantially normal to said pole pieces, said coil structure being energized by variable signaling current and arranged to vibrate substantially independent of mechanical resonances for imparting corresponding vibrations to said sound reproducing diaphragm.

4-. In an electromagnetic sound reproducer an electromagnetic field system including a plurality oi. pole pieces directed toward each other and se nrrated by a narrow gap therebetween, a Hat coil support, means at each side of said electroiuagnetic lield system for flexibly suspending said flat coil, system said means comprising flat sheets of relatively thin flexible material rigidly connected with said flat coil support for permitting move ment of said coil srqgiport in said narrow gap substantially normal to the direction ol' said pole pieces, a sound reproducing diaphragm connected with said fiat coil support and a flat coil member carried by said flat coil support and arranged to be energized by variable signaling current whereby vibrations may be imparted to said sound reproducing diaphragm substantially free of mechanical resonances.

5. In an electromagnetic sound reproducer, a frame structure, an electromagnetic operating mechanism carried by said frame structure including pole pieces directed. toward 1 each other and separated by a relatively narrow gap, a flat coil support disposed in said narrow gap, means carried by said frame structure at opposite ends of said gap for flexibly suspending said fiat coil support for movement in a plane substantially normal to the direction of said pole pieces, a sound reproducing diaphragm flexibly suspended from said frame structure, a connection between said diaphragm and said flat coil support and a winding; carried by said flat coil support and arranged to be energized ,by variable signaling current whereby vibratory motion may be imparted to said flat coil support for transferring corresponding vibrations to said sound reproducingdiaphragm.

6. In an clectrranagrnetic sound reproducing system a frame structure, an electromagnetic.operating mechanism 'arricd by said frame structure having its pole pieces directed toward each other and separated by a relatively narrow gap, spider members located on each side of said frame structure at opposite ends of said gap, a flat coil support carried between said spider members, a sound reprmflucing diapl'iragm flexibly sus pended from said frame structure and connected at its apex with said flat coil support, a winding carried by said lat coil support and arranged to be energized by variable signal currents whereby Vibratory movement in said gap is eftected for imparting corresponding movement to said sound reproducing diaphragm.

7. In an electromagnetic sound reproduc ing system, a frame structure, an electromagnetic operating mechanism carried by said frame structure having its pole pieces directed toward each .other and separated by a relatively narrow gap, means carried by said frame structure at opposite ends of said gap for flexibly suspending a flat coil structure in said gap, a pair of conductive liners for said gap on opposite sides of said coil structure, a sound reproducing diaphragm flexibly suspended from said frame structure and connected with. said flat coil structure and a winding carried by said flat coil structure and arranged to be excited by variable signaling current whereby vibration developed in said fiat coil structure may be imparted to said sound reproducing diaphragm.

8. An electroinagnetie sound reproducer comprising a frame structure, an electromagnetic field system including a plurality of pole pieces directed toward each other and separated. by a narrow gap therebelween, a flat coil. support, spider members located at opposite ends of said narrow gap, said spider members having; a pair of arms secured to said. frame structure and another pair of arms secured to said flat coil support for guiding said coil, support laterally between raid pole pieces, a sound reproducing diaphragm, a connection between said fiat coil. support and said diaphragm and a Winding carried by said flat coil support and arranged to be energized by variable signaling" current, whereby vibrations imparted to said fiat coil support are transmitted to said sound reproducing diaphragm.

In testimony whereof I aliix my signature.

CYRIL A. BRIGHAM. 

